STUDY OF PYROXENE GROUP AND AMOHIBOLE GROUP

STUDY OF PYROXENE GROUP AND AMOHIBOLE GROUP: 

STUDY OF PYROXENE GROUP AND AMOHIBOLE GROUP

PYROXENE GROUP: 

INTRODUCTION It forms another set of important rock-forming minerals. Occurs in good abundance in dark coloured igneous and metamorphic rocks. In fact in ferro-magnesion minerals, pyroxene group occupyfirst place as rock forming group. All of them are closely related in their atomic constitution, crystallisation and general physical properties. PYROXENE GROUP

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Following are members of pyroxene group are of very common occurrence in rocks and hence deserve individual discription

ENSTATITE (Mg SiO3) : 

Crystal system: - orthorhombic (massive, fibrous). Clevage :- prismatic. Colour :- grayish white to greenish white. Hardness:- 5.5 Sp. Gravity:- 3.1 to 3.3 Lustre :- vitreous to pearly. Composition:- MgSiO 3 Optical:- optically (+) Occurrence:- A common constituents of many igneous rock and some metamorphic rock. ENSTATITE (Mg SiO 3 )

HYPERSTHENE (fe, Mg) SiO3: 

Crystal system:- orthorhombic Clevage :- prismatic Colour :- green, olive green to greenish black Hardness:- 5-6 Sp. Gravity:- 3.4-3.5 Lustre :- pearly to vitreous (streak- grey) Composition:- primarily asilicate of magnesium with more than 14% of FeO . Also present alumina in some variety. Optical:- opticallt (-) Occurrence:- found in plutonic rocks like gabbros and norites HYPERSTHENE (fe, Mg) SiO 3

DIOSPIDE Ca Mg(Si2O6) : 

crystal system:-Monoclinic Clevage :- prismatic and distinct. Colour :- light green, grey, colourless . Hardness:- 5 - 6 Sp. Gravity:- 3.27-3.38 Composition:- calcium magnesium silicate with Fe and Mg Occurrence:- it is common constituent of basic and ultra basic igneous rocks. DIOSPIDE Ca Mg(Si 2 O 6 )

AUGITE Ca(Mg,Fe,Al)(Al, SiO)2O6 : 

crystal system:- Monoclinic Clevage :- prismatic Colour :- greyish , green and black. Hardness:- 5 - 6 Sp. Gravity:- 3.25-3.55(depend on iron content) Lustre :- commonly vitreous Composition:- complex Fe-Mg silicate Optical:- optically(+) Occurrence:- a verry common ferro magnesium mineral . The basi and altra basic rock are specially rich in augite . AUGITE Ca(Mg,Fe,Al)(Al, SiO) 2 O 6

AMPHIBOLE GROUP: 

INTRODUCTION Parallel to pyroxene group because many minerals show a striking resemblance to the pyroxene minerals in many of their properties. Also characterized with a double clevage . Hardness between 5-6 Specific gravity from 3 – 3.5 Generally dark in colour . AMPHIBOLE GROUP

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Folowing are some examples of amphibole group

ANTHOPHYLLITE (Mg, Fe)3 (Mg, Fe)3 : 

Crystal system:- orthorhombic Cleavage:- perfect and prismatic Colour :- grey, brownish, greenish Hardness:- 5.5-6 Sp.gravity :- 2.85-3.20 Lustre :- vitreous Optical:- optically(+) Occurrence:- found in metamorphic rocks ANTHOPHYLLITE (Mg, Fe) 3 (Mg, Fe) 3

TREMOLITE Ca2Mg5[(Si4O11]2[OH]2: 

Crystal system:- monoclinic, crystals are long, bladed Cleavage:- prismatic and perfect Colour :- commonly white to light grey. Hardness:- 5.5 6 Sp. Gravity:- 2.9-3 Lustre :- vitreous Optical:- optically(-) Occurance :- igneous and metamorphic rocks. TREMOLITE Ca 2 Mg 5 [(Si 4 O 11 ] 2 [OH] 2

ACTINOLITE Ca2(Mg fe)5[(Si4O11]2[OH]2 : 

Crystal system:- monoclinic Cleavage:- perfect, prismatic Colour :- mostly a green amphibole Hardness:- 5.5-6 Sp.gravity :- 3.1-3.3 ACTINOLITE Ca 2( Mg fe) 5 [(Si 4 O 11 ] 2 [OH] 2

HORNBLENDE Ca2Na(Mg fe)(Al,Fe)[(SiAl)4O11]2[OH]2: 

Crystal system:- monoclinic, crystals long, slender and prismatic Cleavage:- perfect, prismatic Hardness:- 5.5-6 Sp. Gravity;- 3-3.47 Lustre :- vitreous Streak:- white, with greenish tint Composition:- highly variable and complex; broadly an aluminous amphibole Optical:- optically(-) HORNBLENDE Ca 2 Na(Mg fe)(Al,Fe)[(SiAl) 4 O 11 ] 2 [OH] 2

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Occurrence:- it is a common rock forming mineral in igneous and metamorphic rocks. Varites :- about half a dozen varieties of hornblend have been differentiated on the basis of variation in its chemical composition.

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Compaison of pyroxene and amphibole group

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character pyroxene Amphibole crystallisation 1.Orthorhombic, monoclinic 1.Orthorhombic, monoclinic 2. Crystals are commonly short and stout. 2. Crystals are commonly long and slender. cleavage 1.perfect, prismatic 1.perfect, prismatic 2.Cleavage angle is 8 7 degree 2.Cleavage angle is 124 degree physical 1. H=5-6 1. H=5-6 2.Sp.Gr.= 3-3.8 2.Sp.Gr.= 2.8-3.8 3.colour= grey, black, and other dark shades 3.colour= grey, black, and other dark shades Atomic structure 1.silicon= oxygen tetrahedra linked together in chain structure. 1.silicon= oxygen tetrahedra linked together in chain structure. 2.Consist of extensions of single chain of tetrahedra yeilding Si:O ratio of (1:3) 2.Consist of extensions of double chain of tetrahedra yeilding Si:O ratio of (4:11)

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character pyroxene Amphibole chemical Metasilicate with general formula of R. SiO 3 where R= Ca, Mg, Fe, Al etc. Metasilicate but with hydroxyl group and general formula is R[Si 4 O 11 ] 2 [OH] 2 Where R= Ca, Mg, Fe, Al etc. Cross section It appears octagonal with almost right angle cleavage. It appear hexagonal with cleavage angle of 124 degree.

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